libnvdimm fixes for v5.12-rc8

- Fix a regression of read-only handling in the pmem driver.
 
 - Fix a compile warning.
 
 - Fix support for platform cache flush commands on powerpc/papr
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Merge tag 'libnvdimm-fixes-for-5.12-rc8' of git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm

Pull libnvdimm fixes from Dan Williams:
 "The largest change is for a regression that landed during -rc1 for
  block-device read-only handling. Vaibhav found a new use for the
  ability (originally introduced by virtio_pmem) to call back to the
  platform to flush data, but also found an original bug in that
  implementation. Lastly, Arnd cleans up some compile warnings in dax.

  This has all appeared in -next with no reported issues.

  Summary:

   - Fix a regression of read-only handling in the pmem driver

   - Fix a compile warning

   - Fix support for platform cache flush commands on powerpc/papr"

* tag 'libnvdimm-fixes-for-5.12-rc8' of git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm:
  libnvdimm/region: Fix nvdimm_has_flush() to handle ND_REGION_ASYNC
  libnvdimm: Notify disk drivers to revalidate region read-only
  dax: avoid -Wempty-body warnings

include/linux/nd.h

@@ -11,6 +11,7 @@
 
 enum nvdimm_event {
 	NVDIMM_REVALIDATE_POISON,
+	NVDIMM_REVALIDATE_REGION,
 };
 
 enum nvdimm_claim_class {